The present invention relates to a technique for fabricating a group III nitride semiconductor light-emitting device such as an n-side-up light-emitting diode (LED) or a laser diode through the use of an epitaxial wafer wherein a group III nitride semiconductor crystal layer is provided over a p-type silicon (Si) single crystal with a crystal layer comprising a boron phosphide (BP) based material interposed therebetween.
With respect to an epitaxial wafer, which is aimed for the production of group III nitride semiconductor light-emitting devices provided with a group III nitride semiconductor crystal layer, a prior art method for fabricating an epitaxial wafer by using a conductive cubic crystal of Si or the like as a substrate and forming thereon a layer of a group III nitride semiconductor, that is, an AlXGaYInZN (0xe2x89xa6Xxe2x89xa61, 0xe2x89xa6Yxe2x89xa61, 0xe2x89xa6Zxe2x89xa61, X+Y+Z=1.) (Japanese Laid-Open Patent Application No. 11-40850) is known. If a cubic crystal of Si or the like having a diamond structure or a cubic crystal of gallium phosphide (GaP) or the like having a zinc blend structure is used as a substrate, a side plane of a lightemitting device can be easily obtained due to the cleavage properties of the cubic crystal. Further, using a low-resistance p-type or n-type conduction Si single crystal as a substrate, another advantage is that an electrode can be formed easily.
In order to provide a group III nitride semiconductor crystal layer having good crystallinity with few crystal defects on a Si single crystal substrate by reducing the lattice mismatch with the Si single crystal, a technique for forming, on the Si single crystal layer, a BP crystal layer as an underlying layer on which the group III nitride semiconductor crystal layer is formed (Japanese Laid-Open Patent Application No. 11-162848) is disclosed. In addition, on a crystal layer comprising BP having a zinc blend crystal structure, a cubic p-type group III nitride semiconductor layer with a lower resistance compared with a hexagonal crystal is more likely to be formed because of the band structure (Japanese Laid-Open Patent Application No. 2-275682). Such a low-resistance cubic p-type group III nitride semiconductor crystal layer is advantageous for easily fabricating a light-emitting portion with a p-n junction type double hetero (DH) structure of a light-emitting device.
On the other hand, however, a group III nitride semiconductor crystal layer has a tendency to become a hexagonal crystal layer due to its low formation energy. (Refer to the following book written and edited by Isamu Akasaki: xe2x80x9cGroup III Nitride Semiconductor,xe2x80x9d Baifukan Co., Ltd., p. 37, Dec. 8, 1999, first edition.) For this reason, even though using a crystal layer composed of cubic BP as an underlying layer and forming thereon a cubic group III nitride semiconductor crystal layer is intended, once a group III nitride semiconductor crystal layer becomes so thick that the effects thereon of the crystal structure of the underlying layer are weak, a hexagonal group III nitride semiconductor crystal layer is prone to grow. Therefore, a problem that low-resistance p-type group III nitride semiconductor crystal layer, which could be produced with ease when using the characteristics of the band structure of a cubic crystal, cannot be formed consistently as the layer gets thicker exists.
LEDs using a group III nitride semiconductor are broadly divided into the p-side-up type and n-side-up type depending on the layered structures. The p-side-up type LED is an LED wherein an n-type substrate is located at a lower part thereof and an upper cladding layer located above a light-emitting layer comprises a p-type crystal layer. Conversely, the n-side-up type LED refers to an LED wherein a p-type substrate is located at a lower part thereof and an upper cladding layer comprising an n-type crystal layer is disposed above a light-emitting layer. In the n-side-up type LED, the upper cladding layer or a current diffusion layer located thereon is made of an n-type compound semiconductor layer generally having a larger mobility compared with a p-type compound semiconductor layer, and therefore the n-side-up type LED is inherently advantageous for diffusing a device operation current into the light-emitting portion over a wide range. That is, the n-side-up type LED has an advantageous structure for easily obtaining a high-brightness group III nitride semiconductor light-emitting device.
In view of the foregoing, an object of the present invention is to overcome the conventional technical issues and provide a technique of fabricating an n-side-up type group III nitride semiconductor light-emitting device having high brightness. More specifically, in fabricating an n-side-up type group III nitride semiconductor light-emitting device by using an epitaxial wafer comprising a group III nitride semiconductor crystal layer provided over a p-type Si single crystal substrate via a crystal layer comprising a BP based material, the present invention provides a technique for fabricating the n-side-up type group III nitride semiconductor light-emitting device by appropriately combining a cubic group III nitride semiconductor crystal layer, which is advantageous for forming a low-resistance p-type layer, and a hexagonal n-type group III nitride semiconductor crystal layer, which can be easily formed. Further, the present invention provides an n-side-up type group m nitride semiconductor light-emitting device fabricated from an epitaxial wafer, which comprises group III nitride semiconductor crystal layers having different crystal structures, i.e., cubic and hexagonal forms.
The present invention provides a group III nitride semiconductor light-emitting device comprising a substrate comprising a p-type conduction silicon (Si) single crystal, a buffer layer comprising a boron phosphide (BP) based material, which is provided on the substrate, a cubic p-type single crystal layer comprising a BP based material, which is provided on the buffer layer in contact therewith, a cubic p-type group III nitride semiconductor crystal layer, which is provided on the p-type single crystal layer in contact therewith, and a hexagonal n-type group III nitride semiconductor crystal layer provided on the p-type group III nitride semiconductor crystal layer.
In particular, in the present invention, the above-mentioned p-type group III nitride semiconductor crystal layer preferably has a thickness of about 10 nanometer (nm) or more and about 500 nm or less. Further, a dopant for the p-type group III nitride semiconductor crystal layer is preferably at least one selected from a group consisting of zinc (Zn), magnesium (Mg), and carbon (C).
In accordance with the present invention, the above-mentioned cubic p-type group III nitride semiconductor crystal layer and hexagonal n-type group III nitride semiconductor crystal layer are intended to be used for a light-emitting portion of the group III nitride semiconductor light-emitting device.
Further, the present invention provides a method of manufacturing a group III nitride semiconductor light-emitting device comprising the step of successively providing a buffer layer comprising a BP based material, a cubic p-type single crystal layer comprising a BP based material, a cubic p-type group III nitride semiconductor crystal layer, and a hexagonal n-type group III nitride semiconductor crystal layer, in order on a substrate comprising a p-type conduction Si single crystal, wherein the p-type single crystal layer is provided at a temperature higher than the temperature used for providing the buffer layer.
In particular, in the present invention, the temperature for providing the buffer layer is preferably in the range of about 300xc2x0 C. to about 400xc2x0 C.
Further, in the present invention, the temperature for providing the cubic p-type group III nitride semiconductor crystal layer is preferably in the range of about 800xc2x0 C. to about 1000xc2x0 C.
Still further, in the present invention, the temperature for providing the hexagonal n-type group III nitride semiconductor crystal layer is preferably about 1000xc2x0 C. or more.